Collision sensor for fender bumper operated vehicle safety device

ABSTRACT

An impact-responsive switch mounted on a shock-absorbing bumper and having a housing for a bore. An elongate retractable member is axially slidably mounted in the bore to retract to open or close two contacts provided therein when subjected to a collision impact. The elongate retractable member has attached thereto a permanent magnet which, in the retracted position, applies an attractive or repulsive force tending to close or open the two contacts which are hermetically sealed within an evacuated glass tube to prevent degeneration of the contacts. The impactresponsive switch is so positioned on the bumper that the elongate member is subjected to the collision impact upon compression of a resilient member which is interposed between a back plate of a buffer bar and an end plate of a piston rod forming a part of the bumper mechanism.

United States Patent [191 Hirashima et a1.

[11] 3,853,199 [4 Dec. 10, 1974 COLLISION SENSOR FOR FENDER BUMPEROPERATED VEHICLE SAFETY DEVICE [75] Inventors: Kenzo Hirashima; ShunjiMatsui,

both of Yokohama; Yoshikazu Hayakawa, Yokosuka, all of Japan [73]Assignee: Nissan Motor Company, Limited,

' Yokohama City, Japan [22] Filed: Nov. 30, 1972 [21] Appl. No.: 310,943

301 Foreign Application Priority Data Nov. 30, 1971 Japan 46-111870 Apr.28, 1972 Japan 47-49731 [52] US. Cl. 180/91, 180/103, 200/61.08,'

200/61.44, ZOO/61.45 R, ZOO/61.51, 293/4 [51] Int. Cl B60r 21/00, l-lOlh3/16 [58] Field of Search 200/61.45 R, 61.53, 6,

200/16 A, 61.08, 159 A, 166C, 166 BA;

Koepke 335/205 3,495,675 2/1970 Hass et a1 ZOO/61.45 R X 3,654,4124/1972 l-Iaruna et a1. 180/91 X 3,668,355 6/1972 Campbell et a1...200/166 C 3,673,358 6/1972 Harmon 335/206 X 3,699,276 10/1972 Atakkaan200/16 A 3,704,514 12/1972 Fuchs et al 200/166 C X 3,718,877 2/1973Matsushima... 335/205 3,744,588 7/1973 Nave, Sr. 180/103 X 3,778,57212/1973 Matsui et a1. ZOO/61.5 X 3,793,498 2/1974 Matsui ct a1.ZOO/61.45 R

FOREIGN PATENTS OR APPLICATIONS 507,283 12/1951 Belgium 293/4 PrimaryExaminer.1ames R. Scott [5 7] ABSTRACT elongate retractable member isaxially' slidably mounted in the bore to retract to open or close twocontacts provided therein when subjected to a collision impact. Theelongate retractable member has attached thereto a permanent magnetwhich, in the retracted position, applies an attractive or repulsiveforce tending to close or open the two contacts-which are hermeticallysealed within an evacuated glass tube to prevent degeneration of thecontacts. The impactresponsive switch is so positioned on the bumperthat the elongate member is subjected to the collision impact uponcompression of a resilient member which is interposed between abackplate of a buffer barand an end plate of a piston rod forming a part ofthe bumper mechanism. a

15 Claims, 16 Drawing Figures COLLISION SENSOR FOR FENDER BUMPEROPERATED VEHICLE SAFETY DEVICE This invention relates generally to motorvehicle safety devices and more particularly to an improved switchmechanism of the impact-responsive type to be mounted on ashock-absorbing bumper of a motor vehicle.

Heretofore, many safety devices and collision sensors have beendeveloped for use on motor vehicles. Such collision sensor usuallycomprises a switch mechanism which is adapted to be closed or openedupon sensing a collision condition. It has been found in the art that inorder to successfully protect occupants from injuries the switch isrequired to be closed or opened within one or two milliseconds after acollision begins. Another requirement to be satisfied by the switchmechanism of this kind is that it cannot be readily actuated by anythingelse than a collision.

It is an object of the present invention to provide an improved switchmechanism for a motor vehicle safety device that meets the above-statedrequirements for successfully protecting occupants from injuries at thetime of a collision.

Another object of the present invention is to provide an improved switchmechanism which is adapted for use on a shock-absorbing bumper of amotorvehicle to sense an impact upon the bumper resulting from a collision ofthe vehicle. I

It is a further object of the present invention to provide an improvedswitch mechanism which is adapted for use with an inertia switch of aknown type to insure a reliable detection of a collision of the vehicle.

It is still another object'of the present invention to provide animproved switch mechanism-which is simple in construction, inexpensiveto manufacture and durable in use.

These and other objects will be readily apparent from the followingdescription of the invention taken in conjunction with accompanyingdrawings, in which: I

FIG. 1 is a side elevation, partly in section, of a shock-absorbingbumper of a motor vehicle on which a switch mechanism according to theinvention is mounted; I v

FIG. 2 is an enlarged sectional view of the connection between a bufferbar and a piston rod of the bumper mechanism the switch mechanismv ofthe invention being shown as mounted on an end plate of the piston rod;

FIG. '3 is a perspective view. with a schematic diagram of theassociatedelectrical circuit, of a shockabsorbing' bumper according to theinvention;

FIG. 4 is a longitudinal sectional view ofa typical switch mechanismaccording to the invention;

FIG. 5 is a view showing the manner in which the switch mechanism of theinvention is mounted on the buffer bar of the bumper mechanism;

FIG. 6 is a view of a modification of the switch mechanism of FIG. 4;

FIG. 7 is an illustration of a further embodiment of the switchmechanism according to the invention;

FIG. 8 is a view of a typical hermetically sealed' an inertia switchemployed in combination with the switch mechanism of the invention.

A simplified schematic diagram illustrating a preferred overallarrangement of a shock-absorbing bumper to which the sensor or switchmechanism of the invention is applied is shown in FIG. 1. The bumpercomprises an impact member, such as a buffer bar 10 extending crosswiseand horizontally of the vehicle in front of the front wheels or in theback of the rear wheels. The buffer bar 10 is of profiled steel typehaving a web portion 10a and upper and lower inwardly directed flanges10b. Affixed on the outer surface of the web portion 10a is an elongateplate-like member 13 of urethan foam or other suitable material thatserves to lessen impacts upon pedestrians which could otherwise causecritical physical damages to them at the time of a collision. A backplate or impact receiving member 15 is provided which extends betweenthe upper and lower flanges 10b of the buffer plate 10, the upper andlower ends of the back plate 15 being secured to the inner surfaces ofthe upper and lower flanges 10b, respectively. by welding or othersuitable method. The back plate 15 has one or more openings 17 formedtherein (see FIG. 2) for securing thereto a piston 'rod which forms partof a shock absorbing mounting 21.

The shock absorbing mounting 21 is preferably of the hydraulic cushiontype and comprises a cylinder 23, a

piston (not shown) axially movable within the cylinder 23, and thepiston rod 25 extending from the piston toward the buffer bar 10. Thecylinder 23 is secured-on a longitudinally disposed frame portion or aside bar 27 of a vehicle chassis by means of bracket members 29.

As is best seen in FIG. 2, thepiston rod 25 has mounted thereon orintegrally formed therewith an end plate 31 which is secured to the backplate 15 by a bolt and nut assembly 33 with a resilient plate member 35interposed therebetween. The resilient member 35 is made of foam rubberor any other suitable material that is sufficiently resilient to absorbshearing stresses as well as compression stresses. The opening 17 in theback plate 15, and its corresponding openings 37 and 39 formed in theend plate 31 and the resilient member 35, respectively, are so arrangedas to have same diameters which are somewhat larger than the outerdiameter of a bolt 33a so as to provide slight lateral movement or playof the back plate 15 relative to the end plate 31.

The sensor or switch mechanism according to the invention is generallydesignated by and is mounted on the end plate 31 of the piston rod 25 tosense an impact upon the buffer bar 10 at the time of a collision. Atypical example of the switch mechanism is shown in FIG. 4, whichcomprises a casing or housing 52 having a chamber 54 formed therein andan axial bore 56 extending from the chamber 54. An elongate retractablemember 58 is mounted in the axial bore 56 slidably movable therein. Theelongate member 58 has secured at its inner end a plate 60 ofelectrically conductive material for normally providing an electric pathbetween two contacts 62 and 63 provided in the chamber 54 on both sidesof the axial bore 56. The chamber 54 is also provided with a spring seat65 for receiving a coil or helical spring 67 which acts to apply a forceon the end plate 60 to urge the elongate retractable member 58 to itsfully extended position shown in FIG. 4. Connections to the contacts 62and 63 are made by wires 72 and 73, respectively, which are connected toa vehicle safety device (not shown).

As seen in FIG. 2, the resilient member 35 and the end plate 31 of thepiston rod 25 have formed therein aligned openings 75 and 76,respectively, which are of identical diameter somewhat larger than theouter diameter of the elongate retractable member 58. The sensor orswitch mechanism 50 is secured to the surface of the end plate 31opposite to the resilient member 35 by suitable means (not shown), withthe elongate retractable member 58 extending through the alignedopenings 75 and 76. It should be noted that the length of the elongatemember 58 is such that there is a gap left between the tip of theelongate member 58 and the surface of the back plate 15 under normalconditions.

In the operation of the arrangement shown in FIGS. 1, 2, 3and 4, whenthe buffer bar is subjected to a strong impact due to a violentcollision of the vehicle against'another one or a stationary structurein the path of advance, the buffer bar 10 is deformed instantlyinwardly, causing the resilient member 35 to be compressed. Even if acollision other than a headon one is encountered by the vehicle, theresilient member 35 is compressed by the back plate of the buffer bar10,

.since the plate 15 is connected with the end plate 31 permitting aslight lateral movement relative to each other. as described above. Whenthis occurs, the elongate member 58 is urged into the housing 52 by theback plate 15, so that the end plate 60 of the elongated member 58 ismoved in a right-hand direction as viewed in FIG. 4 against the actionof the spring 67.

This will disconnect the contacts 62 and 63 from each FIG. 6 illustratesanother preferred embodiment of the sensor or switch mechanism accordingto the invention which is different from that of FIG. 4 in that a leafspring 85 is employed in place of the coil or helical spring 67. Theleaf spring 85 is preloaded so as to normally urge the elongate member58' to its fully extended position through a protuberance 87 provided onthe end plate 60'. The leaf spring 85 is made of electrically conductivematerial and is normally kept in contact with afixed contact 89 providedin the housing 52. When the elongate member 58 is caused to retract intothe housing 52' due to an impact thereon resulting from a collision ofthe vehicle, the leaf spring is moved away from the fixed contact 89resulting in actuation of the vehicle safety device.

FIG. 7 illustrates a further embodiment of the switch mechanismaccording to the invention which includes a permanent magnet 90 formagnetically actuating a hermetically sealed switch 92. As illustrated,the sensor or switch mechanism also includes a casing or housing 94having a chamber 96 formed therein and an axial bore 98 extending fromthe chamber 96. An elongate retractable member 100 is axially slidablymounted in the axial bore 98 and is normally biased to its fullyextended position by means of a spring 102. The permanent magnet 90 ismounted at the inner end of the elongate member 100 and, when theelongate member 100 is moved to its retracted position, the magnet 90 isplaced in a position immediately above the hermetically sealed switch92, where it actuates the switch 92. The switch 92 is disposed withinthe chamber 96 longitudinally of the housing 94 to extend along thespring 102.

The switch 92, as best seen in FIG. 8, comprises an elongate hollow tube106 of electrically insulating material such as glass, containing inertgas. Alternatively, the hollow tube 106 may be evacuated to preventdegeneration of contacts provided therein. A contact 108 extends intothe interior of the tube 106 from the left exterior side thereof and ispreferably made of nonmagnetic material such as aluminum or copper.Another contact 110 is made of resilient and magnetic material andextends into the tube 106 from the right exterior side thereof towardthe contact 108. The contact 110 is preloaded so that the tip thereof isnormally held in contact with the lower surface of the contact 108. Whenthe permanent magnet 90 is moved from the position indicated by thesolid line 90a to that indicated by the broken line 90b in response to acollision, the tip of the contact 110 is moved downwards away from thecontact 108 due to a repulsive force applied thereto by the magnet 90.

FIG. 9 illustrates the sensor or switch mechanism according to theinvention which includes a cover mounted on the housing 52 to enclosethe elongate retractable member 58. The cover 120 serves to prevent theentrance of dirt, water or other foreign matter into the axial bore 56(not identified) which would otherwise cause corrosion of contacts orlead to malfunction of the switch mechanism.

FIG. 10 illustrates a further preferred embodiment of the sensor orswitch mechanism according to the invention which sensor is generally ofthe pneumatically actuated type. A casing or housing has formed thereina chamber 132 which is divided into two axial compartments 132a and1321; by a partition member 134 provided in the chamber 132. A piston136 is axially slidably mounted within the compartment 132a and has apiston rod 138 extending externally therefrom through an opening formedin the housing 130. The partition member 134 is formed in the centerthereof with an opening 140 which communicates with the interior of abellows member 142 provided within the compartment 132a on the partitionmember 134. The bellows member 142 is secured to a plate member 144through which the bellows member 142 is normally compressed to itscontracted condition by means of a spring 146 provided between thepartition member 134 and the plate member 144. The plate member 144 isof electrically conductive material and is normally engaging a contact148 leading to a'terminal 150. A fixed contact 152 is provided betweenthe partition member 134 and the plate member 144 and is normally heldin abutting engagement with the conductive plate member 144. Anotherterminal 154 is provided leading to the fixed contact 152. When acollision takes place, the piston rod 138 is urged into the housing tomove the piston 136 in a right-hand direction as viewed in FIG. 10,thereby causing the bellows member 142 to expand. Expansion of thebellows member 142 moves the plate member 144 away from the fixedcontact 152 against the action of the spring 146, so that an electriccircuit between the terminals and 154 is opened.

FIG. 11 illustrates still another preferred embodiment of the sensor orswitch mechanism according to the invention which is similar to thatshown in FIG. 4 except that the elongate retractable member 58 isnormally held in its fullyextended position by means of a magnet insteadof the spring 67'(see FIG. 4). The magnet 160 may be a permanent magnetor an electromagnet which is capable of holding the elongate member 58in the-position shown without being affected by rather light impacts notresulting from a collision of the vehicle.

FIG. .12 illustrates a still .further preferred embodiment of the sensoror switch mechanism accordingto the invention which is also similar tothat shown in FIG. 4 except that the contacts 62 and 63 are replaced bya tubular contact member 165. As is best seen in FIG. 13, the tubularcontact member comprises two elongate portions 165a and l65b which aremade of glass or other suitable material having thereon a coating ofelectrically conductivemate'rial. When a collision takes place, theportions 165:: and 16512 shatter, interrupting an electric path betweenterminals connected thereto.

'The contact member 165 may be formed of carbon,

and further, it may be formed in a circular fashion as seenin FIGQM. I

The switch mechanisms as shown and described 7 above are employedseparately or in combination with other collision-sensitive switch typesin order to insure a reliable sensing of a collision condition whichcould possibly cause critical physical injuries to the vehicleoccupants.

FIG. 15 illustrates a typical arrangement of the inertia switch which isof the sensitivity-modulating type. The switch 170 includes a weight 174of magnetic material which is suspended by a conductive wire 176 leadingto a terminal 178. The weight 174 is normally held in abuttingengagement with a permanent magnet I80 and an electromagnet 182 which isenergized by a battery 184 through the switch mechanism 50 of theinvention. Since, in normal condition. the weight 174 is held in theposition shown with two forces exerted by the permanent magnet I80 andthe electromagnet 182, it will be appreciated that even a rapidacceleration or deceleration of the vehicle during normal driving cannotcause movement of the weightl74 away from the magnets and 182. However,when a collision occurs, the switch mechanism 50 is opened, reducing tozero the force exerted on the weight 174 by the electromagnet 182, sothat the weight 174 is moved into contact with a fixed contact 186 witha decreased force of inertia applied to the weight 174. It will beappreciated that with this arrangement it is possible to keep at arelatively low value the'magnitude of deceleration above which theinertia switch 17 is actuated at the time of a collision.

FIG. 16 illustrates another arrangement of the inertia switch 170' whichis adapted for use with the sensor or switch mechanism of the invention.The inertia switch 170 comprises a tubular member or housing 190 havingan internal cylindrical bore 192 f0 formed therein within which a weightin the form of a sphere 194 is disposed. The weight 194 is normally heldagainst one end wall of the cylidrical bore 192 by a contact member 196which in turn is urged in a left-hand direction as viewed in FIG. 16 bya spring 198 provided within the cylindrical bore 192. Extendinginwardly from the other end wall of the bore 192 toward the contactmember 196 is another contact member 200 which leads to a terminal 202.The spring 198 is of electrically conductive material, connecting thecontact member 196 to a terminal 204. The inertia switch 170' alsoincludes an electromagnet 206 provided in the left end portion of thetubular member 190 adjacent the spherical weight 194. The electromagnet206 is connected in series with the switch mechanism 50 of the presentinmembers it should be understood that the invention is not restrictedto either one of the two types. It would be possible to readily modifythe switch mechanism from a closed-open to open-closed or fromopen-closed to closed-open type. In this connection, it should be notedthat the switch mechanism which is opened when a collision takes placeis characterized by a quick response in that even a slight movement ofthe movable contact causes itself to be disconnected fromthe fixedcontact.

Furthermore, it should be noted that with the employment of thehermetically sealed switch 92 shown in FIG. 8, the switch mechanism ofthe invention has an increased durability in use since the internallymounted contacts 108 and 110 are prevented from exposure to the air.

Still furthermore, it should be noted that since the piston rod 25 ofthe shock absorbing mounting 21 is connected with the back plate 15 ofthe buffer bar 10 in a manner to permit slight lateral movement relativeto each other, the sensor or switch mechanism of the invention isresponsive toa collision other than a headon collision as well.

What is claimed is: l. In a motor vehicle having a safety deviceactuable in response to a collision signal, at least one shock absorbingbumper, which bumper includes an impact receiving member extendingcrosswise horizontally of the vehicle, a cylinder disposedlongitudinally of the vehicle and secured to the vehicle's body, apiston axially slidable in a bore of the cylinder, a piston rodextending externally from the piston and having one end secured to theimpact receiving member, the piston rod being adapted to be withdrawninto the cylinder when said impact receiving member deforms uponcollision against a solid obstacle, and a resilient member disapparatuscomprising, in

means defining aligned niches in said one end of said piston rodand saidresilient member and lying adjacent said insulated housing,

an elongate actuating member axially slidably mounted in the cavity andextending externally of said housing, said elongated actuating memberbeing arranged to normally extend through said niche in said one end ofsaid piston rod into said niche formed in said'resilient member but tobe withdrawn into said housingupon compression of the resilient memberresulting from the collision,

a fixed contact disposed in said cavity, and

a movable contact which is associated with said elongate actuatingmember, disposed in said cavity and normally held in contact with thefixed contact, the

movable contact being movable to disengage from the fixed contact inresponse to the withdrawal movement of said elongate actuating member toopen said first electric circuit;

anda normally open, inertia responsive switch forming part of a secondelectric circuit connected with the safety'device for producing thecollision signal upon closure thereof, said inertia responsive switchincluding,

an insulated housing mounted on the vehicle body adjacent 'to saidimpact receiving member, the housing defining a cavity therein,

an inertia-responsive magnetic weight located in said cavity formovement in a longitudinal direction of the vehicle body in response tothe inertia applied to the body during the collision,

a movable contact disposed on said inertia weight,

a fixed contact disposed in said housing adjacent to the movablecontact, the fixed contact being positioned in a path of the inertiaresponsive movement of said inertia weight,

means applying a force to usually hold said movable contact apart fromsaid fixed contact, the force being overcome by the inertia force at apredeterv mined degree, and electromagnetic means mounted in the cavityof said inertia responsive switch housing and situated adjaonly byovercoming the force of said force applying means to close said secondelectric circuit.

2. An apparatus according to claim 1, in which said movable contact ofthe deformation responsive switch is disposed on the inner end of saidelongate actuating member.

3. An apparatus according to claim 2, further comprising means to keepsaid elongate actuating member at its extended position.

4. An apparatus according to claim 3, in which said means to keep saidelongate actuating member at its extended position is a spiral springdisposed between a wall of said cavity and said elongate actuatingmember and preloaded to urge the actuating member toward the extendedposition.

5. An apparatus according to claim 3, in which said means to keep saidelongate actuating member at its extended position is plate springhaving one end fixed to a wall of said cavity and preloaded to urge theactuating member toward the extended position.

6. An apparatus according to claim 3, in which said means to keep saidelongate actuating member at its extended position is a permanent magnetdisposed on said housing to exert an attractive force upon said movablecontact on said actuating member to urge it toward the extendedposition.

7. An apparatus according to claim 2, in which said fixed contact of thedeformation responsive switch is a tubular member of glass coatedthereon with an electrically conductive material and disposed in contactwith said movable contact, said tubular member being adapted to bebroken by said actuating member when said actuating member is withdrawnthereby cutting off the electric connection of said movable contact withsaid fixed contact.

8. An apparatus according to claim 1, in which said deformationresponsive switch further comprises a permanent magnet provided on saidelongate actuating member.

9. An apparatus according to claim 8, in which said movable contact andsaid fixed contact of the deformation responsive switch form a reedenclosed in a fluidtight tube disposed adjacent to said permanentmagnet.

10. An apparatus according to claim 1, in which said cavity of saidhousing of said deformation responsive switch is divided into a firstcompartment and a second compartment by a partition member, andaccommodates therein a piston secured to the inner end of said elongateactuating member, said piston being axially slidable in the firstcompartment, and a bellows member provided within the second compartmentand communicating with the first compartment through an opening formedin the partition member, and in which said movable contact is disposedon the bellows member for movement therewith and said fixed contact isprovided in the second compartment normally in contact with said fixedcontact by a tension spring, whereby upon compression of said bellowsmember, said movable contact is removed from said fixed contact.

11. An apparatus according to claim 1, in which said inertia weight ofthe inertia responsive switch is of a pendent type hanging from the topwall of the housing by a flexible wire.

12. An apparatus according to claim 11, in which said force applyingmeans is a permanent magnet disposed adjacent to said inertia weight onthe side site to the position of said fixed contact.

13. An apparatus according to claim 1, in which said force applyingmeans is a spring within said cavity ex-- tending in. the longitudinaldirection of the vehicle and having one end anchored to the movablecontact on said inertia weight to urge ittoward the electromagneticmeans.

14. An apparatus according to claim 13, in which said inertia weight isa spherical member held in position by said spring.

15. A collision sensor for sensing a collision condition of a motorvehicle to actuate a safety device mounted thereon, said collisionsensor being mounted on a shock-absorbing bumper which includes animpact receiving member extending crosswise horizontally of the vehicle,a cylinder extending longitudinally of the vehicle and secured to thevehicle's body, a piston axially slidable in the cylinder, a piston rodextending externally from the piston and connected with the impactreceiving member, and a resilient member provided on the impactreceiving member to partially absorb an impact resulting from acollision, said collision sensor comprising: a housing having a boreformed therein; an elongate actuating member axially and slidablymounted in the bore and extending externally of said oppohousing, saidelongate actuating member being arranged to normally extend into a nicheformed in the resilient member but to be retracted into said housingupon compression of the resilient member resulting from a collision;biasing means for normally biasing said elongate actuating member to itsextended position; switch means provided in said housing for actuatingthe safety device when said elongate actuating member is forcibly movedto its retracted position, said housing having a chamber divided intofirst and second compartments by a partition member; and said elon gateactuating member has a piston secured to the inner end thereof, thepiston being axially slidable in the first axial compartment; and abellows member is provided within the second compartment andcommunicates with the first compartment through an opening formed in thepartition member; and said switch means comprises a movable contactsecured to the bellows member for movement therewith, and a fixedcontact provided in the second compartment; and said biasing meanscomprises a spring provided between the partition member and the movablecontact to normally keep the bellows member in a contracted condition,the movable contact being kept in contact with the fixed contact whenthe bellows member is contracted.

1. In a motor vehicle having a safety device actuable in response to acollision signal, at least one shock absorbing bumper, which bumperincludes an impact receiving member extending crosswise horizontally ofthe vehicle, a cylinder disposed longitudinally of the vehicle andsecured to the vehicle''s body, a piston axially slidable in a bore ofthe cylinder, a piston rod extending externally from the piston andhaving one end secured to the impact receiving member, the piston rodbeing adapted to be withdrawn into the cylinder when said impactreceiving member deforms upon collision against a solid obstacle, and aresilient member disposed between the impact receiving member and thepiston rod to partially absorb an impact resulting from a collision, acollision signal producing apparatus comprising, in combination, anormally closed, vehicle deformation responsive switch forming part of afirst electric circuit, said deformation responsive switch including aninsulated housing mounted adjacent said resilient member and disposed onsaid one end of the piston rod, the housing defining a cavity formedtherein, means defining aligned niches in said one end of said pistonrod and said resilient member and lying adjacent said insulated housing,an elongate actuating member axially slidably mounted in the cavity andextending externally of said housing, said elongated actuating memberbeing arranged to normally extend through said niche in said one end ofsaid piston rod into said niche formed in said resilient member but tobe withdrawn into said housing upon compression of the resilient memberresulting from the collision, a fixed contact disposed in said cavity,and a movable contact which is associated with said elongate actuatingmember, disposed in said cavity and normally held in contact with thefixed contact, the movable contact being movable to disengage from thefixed contact in response to the withdrawal movement of said elongateactuating member to open said first electric circuit; and a normallyopen, inertia responsive switch forming part of a second electriccircuit connected with the safety device for producing the collisionsignal upon closure thereof, said inertia responsive switch including,an insulated housing mounted on the vehicle body adjacent to said impactreceiving member, the housing defining a cavity therein, aninertia-responsive magnetic weight located in said cavity for movementin a longitudinal direction of the vehicle body in response to theinertia applied to the body during the collision, a movable contactdisposed on said inertia weight, a fixed contact disposed in saidhousing adjacent to the movable contact, the fixed contact beingpositioned in a path of the inertia responsive movement of said inertiaweight, means applying a force to usually hold said movable contactapart from said fixed contact, the force being overcome by the inertiaforce at a predetermined degree, and electromagnetic means mounted inthe cavity of said inertia responsive switch housing and situatedadjacent to the inertia weight on the side opposite to the position ofsaid fixed contact to exert, upon energization thereof, an attractiveforce upon said inertia weight to hold the movable contact apart fromsaid fixed contact, said electromagnetic means being connected with thefirst electric circuit and adapted to be deenergized upon opening ofsaid first electric circuit; whereby said movable contact of the inertiaweight is allowed to engage with the fixed contact at a predetermineddegree of collision which is enough to open said vehicle deformationresponsive switch, only by overcoming the force of said force applyingmeans to close said second electric circuit.
 2. An apparatus accordingto claim 1, in which said movable contact of the deformation responsiveswitch is disposed on the inner end of said elongate actuating member.3. An apparatus according to claim 2, further comprising means to keepsaid elongate actuating member at its extended position.
 4. An apparatusaccording to claim 3, in which said means to keep said elongateactuating member at its extended position is a spiral spring disposedbetween a wall of said cavity and said elongate actuating member andpreloaded to urge the actuating member toward the extended position. 5.An apparatus according to claim 3, in which said means to keep saidelongate actuating member at its extended position is plate springhaving one end fixed to a wall of said cavity and preloaded to urge theactuating member toward the extended position.
 6. An apparatus accordingto claim 3, in which said means to keep said elongate actuating memberat its extended position is a permanent magnet disposed on said housingto exert an attractive force upon said movable contact on said actuatingmember to urge it toward the extended position.
 7. An apparatusaccording to claim 2, in which said fixed contact of the deformationresponsive switch is a tubular member of glass coated thereon with anelectrically conductive material and disposed in contact with saidmovable contact, said tubular member being adapted to be broken by saidactuating member when said actuating member is withdrawn thereby cuttingoff the electric connection of said movable contact with said fixedcontact.
 8. An apparatus according to claim 1, in which said deformationresponsive switch further comprises a permanent magnet provided on saidelongate actuating member.
 9. An apparatus according to claim 8, inwhich said movable contact and said fixed contact of the deformationresponsive switch form a reed enclosed in a fluid-tight tube disposedadjacent to said permanent magnet.
 10. An apparatus according to claim1, in which said cavity of said housing of said deformation responsiveswitch is divided into a first compartment and a second compartment by apartition member, and accommodates therein a piston secured to the innerend of said elongate actuating member, said piston being axiallyslidable in the first compartment, and a bellows member provided withinthe second compartment and communicating with the first compartmentthrough an opening formed in the partition member, and in which saidmovable contact is disposed on the bellows member for movement therewithand said fixed contact is provided in the second compartment normally incontact with said fixed contact by a tension spring, whereby uponcompression of said bellows member, said movable contact is removed fromsaid fixed contact.
 11. An apparatus according to claim 1, in which saidinertia weight of the inertia responsive switch is of a pendent typehanging from the top wall of the housing by a flexible wire.
 12. Anapparatus according to claim 11, in which said force applying means is apermanent magnet disposed adjacent to said inertia weight on the sideopposite to the position of said fixed contact.
 13. An apparatusaccording to claim 1, in which said force applying means is a springwithin said cavity extending in the longitudinal direction of thevehicle and having one end anchored to the movable contact on saidinertia weight to urge it toward the electromagnetic means.
 14. Anapparatus according to claim 13, in which said inertia weight is aspherical member held in position by said spring.
 15. A collision sensorfor sensing a collision condition of a motor vehicle to actuate a safetydevice mounted thereon, said collision sensor being mounted on ashock-absorbing bumper which includes an impact receiving memberextending crosswise horizontally of the vehicle, a cylinder extendinglongitudinally of the vehicle and secured to the vehicle''s body, apiston axially slidable in the cylinder, a piston rod extendingexternally from the piston and connected with the impact receivingmember, and a resilient member provided on the impact receiving memberto partially absorb an impact resulting from a collision, said collisionsensor comprising: a housing having a bore formed therein; an elongateactuating member axially and slidably mounted in the bore and extendingexternally of said housing, said elongate actuating member beingarranged to normally extend into a niche formed in the resilient memberbut to be retracted into said housing upon compression of the resilientmember resulting from a collision; biasing means for normally biasingsaid elongate actuating member to its extended position; switch meansprovided in said housing for actuating the safety device when saidelongate actuating member is forcibly moved to its retracted position,said housing having a chamber divided into first and second compartmentsby a partition member; and said elongate actuating member has a pistonsecured to the inner end thereof, the piston being axially slidable inthe first axial compartment; and a bellows member is provided within thesecond compartment and communicates with the first compartment throughan opening formed in the partition member; and said switch meanscomprises a movable contact secured to the bellows member for movementtherewith, and a fixed contact provided in the second compartment; andsaid biasing means comprises a spring provided between the partitionmember and the movable contact to normally keep the bellows member in acontracted condition, the movable contact being kept in contact with thefixed contact when the bellows member is contracted.